The invention relates to a microkeratotome for the dissection of lamellae of corneal tissue, which has been conceived with characteristics that make it feasible to submerge it in sterilizing fluids for a practical and fast sterilization of the parts other than those of the mechanical transmission system which this type of apparatus includes, in order to reduce the time or interval between cornea-sectioning operations in which it is used, above all in cases where both eyes of the same patient are being operated on. The microkeratotome has means that make complete transparency possible in the cutting area, incorporating likewise an electronic unit with several cutting programmes to be selected according to the keratometry.
It is equally an object of the invention to provide a microkeratotome which gives optimal visibility to the surgeon during an operation, by virtue of the fact that the side pieces of the head have been made with a small height, and also the incorporation of a transparent plate in correspondence with the cutting area. Also, greater control during an operation is achieved by the microkeratotome of the invention due to the fact that the corresponding suction ring which immobilizes the eyeball has a specific size and design, being provided with a peripheral channel which uniformly and firmly distributes the vacuum pressure by means of which the eyeball is immobilized.
In 1949 Dr. Jose Barraquer, in Columbia, suggested that sight problems could be corrected by a surgical operation to change the curvature of the cornea. In its origins the procedure consisted of cutting a thin section from the frontal part of the cornea and subsequently freezing it to give the desired shape using a cryogenic lathe and then thawing it before implanting it.
The instrument used to make sections in the cornea is known as a Microkeratotome and the system upon which its action is based today is that of cutting a lamella of the desired thickness without complete detachment from the rest and forming a hinge which, when folded back, leaves an area of operation free for the laser, with which the curvature of the cornea will be modified by its action, and is subsequently refolded for cicatrization to take place.
In the last thirty years Microkeratotomes have been used with the aim of obtaining corneal lamellae of the desired size and thickness. An apparatus which immobilizes the eye has always been used, and another one which, in the manner of a "carpenter's plane", moves and cuts the lamella.
In the first models, the cutting apparatus was moved manually over the fixing ring.
There were, among others, three main problems:
1. The movement did not always follow the desired direction. PA1 2. Manual movement did not provide a uniform speed of advance and this affects the thickness of the lamella obtained (the faster the advance, the less thickness obtained, and vice versa). PA1 3. If the cutting part is raised above the plane of the eyeball immobilizer ring, the lamella is cut at that point, causing a serious complication.
Later, a rail was added to the fixing ring to act as a guide for the cutting part. In other variants two guides were introduced which prevented movements other than in the desired direction. In these models, the problems arising from manual movement with a non-uniform speed continued and the problem of undesired stoppages of the cutting part arose, due to blockages between the rails, which caused significant irregularities in the surface that was being cut.
Automatic movement of the cutting apparatus upon the ring appeared subsequently and with it the differences in thickness were eliminated, as the speed is uniform; some of these apparatus were even equipped with a programmable stop. The problems observed with the automatic model are:
Stoppages of the cutting part before it reaches the end of its path, caused by particles introduced between the two parts or between the gears of the cutting part, or due to mechanical or electrical failure of the system. This forces surgery to be suspended.
Oscillation speed of the blade insufficient for the speed with which the cutting part moves, which produces irregularities in the cutting surface and the edges.
Failure of the suction system due to faults in the pump (of the carbon blade type), or because the conjunctiva closes the hole through which vacuum pressure is applied to the eye.
An interchangeable front plate which makes it possible for the surgeon to forget to put it on, in which case the cutting thickness, being greater than that of the cornea, causes the eyeball to be pierced and serious damage to the internal structures.
Cutting diameter insufficient for some kinds of surgery.
Frequent failures in the movement system, situated in the motor, or in the transmission system due to its mechanical stopping system which causes the motor to overload and significant strain on the transmission. Water entering the transmission also causes it to deteriorate.
When the suction fails, the system does not detect it, and as it continues to cut it cuts the lamella with a shorter length, causing corneal scars.
Play in the movement system together with the fact that the dragging mechanism is produced on only one side tends to cause stoppages in the advance before reaching the end of the path.
While the advance is underway, the shape of the cutting part prevents the surgeon from seeing at what level it is taking place.
Other systems appeared which attempted to remedy some of the problems described, but they provided a cut of poor quality due to the fact that the position of the blade was parallel to the cutting plane.
Other systems provide manual movement, with the problems already mentioned and with a greater blade oscillation speed provided by a turbine system powered by pressurized nitrogen.
The object of the present invention is precisely to devise a Microkeratotome which overcomes the above-mentioned problems and incorporates qualities which markedly improve both the cutting quality and the control, handling, practicality and performance at the disposal of the surgeon.